Large scale mining of materials tends to be an energy intensive endeavor. In many open cast mines, a fleet of large mining trucks may operate almost continuously to transport ore and/or overburden from an extraction area to a dump or processing site. Many such mining trucks are operated via diesel powered engines using either a direct drive strategy or a diesel-electric drive system. As with many other heavy equipment systems, fuel costs for mining trucks can be substantial. Moreover, many mines are located in remote locations, and the costs associated with transporting fuel to the mine site can add significantly to the operational expense. Even obtaining sufficient fuel supplies can sometimes be challenging, regardless of cost. For these and other reasons, engineers in the mining industry and mining equipment manufacturers are continually searching for ways to reduce fuel consumption. Given the historical price volatility of commodities, of which mined materials and petroleum fuels are both examples, as well as variation in geology and topography among mine sites, the economics of supplying and consuming energy for mining activities tends to be complex and highly variable.
For decades, mine operators have experimented with the use of electrical power generated onsite or supplied from a utility grid, to power mining equipment. Onsite electrical power generation has similar costs and availability concerns to refueling equipment directly via petroleum fuels. Due to the remoteness of many mines and other factors, Supplying electrical power from a grid, even over relatively long distances, has proven consistently advantageous for at least some mines as compared to reliance on petroleum fuels alone. Electrical power costs can nevertheless vary due to market fluctuations, as well as varying from mine to mine depending upon regional availability of fossil fuels, geothermal or hydroelectrical power, or other native or obtainable sources of energy for electrical power generation. Thus, even where electrical powering of mining equipment is viable, there remains ample motivation to use it as efficiently as possible, both to control costs and optimize predictability in the face of uncertain economics.
While first proposed decades ago, one contemporary use of electrical power at mine sites is a trolley system having an overhead trolley line to provide electrical power to assist mining trucks, particularly when traveling loaded on uphill grades. Many open cast mines include a haul road extending from an extraction site for ore to a remote dumpsite or processing location. The mining trucks used at such sites may need to travel an uphill grade on a haul road that is several kilometers long, or possibly even longer. It will be appreciated that the use of diesel or other petroleum fuels, such as liquefied natural gas, to propel mining trucks loaded with literally hundreds of tons of ore up such grades can be quite costly, and thus trolley systems have received renewed interest in recent years. A typical mining truck may have at least four different modes of operation. Among these are utilizing onboard electrical systems for propelling or retarding motion of the truck, and trolley based propulsion or even trolley retarding in which electrical power generated by retarding the truck is fed back into the trolley grid. Facilitating all of these modes, and maybe others, can require a DC link topology with multiple different contactors that each can be put in either an open circuit configuration or a closed circuit configuration. For instance, U.S. Pat. No. 6,646,360 shows a DC link topology with at least five contactors to facilitate different operational modes.
The present disclosure is directed toward one or more of the problems set forth above and to providing simpler topology for DC links in certain mining trucks.